Methacrylic resins, represented by poly(methyl methacrylate) (PMMA), are used in a wide variety of fields due to their high transparency, such as optical materials, automotive parts, building materials, lenses, household goods, OA equipment, and lighting devices.
Especially, recently their use in automotive applications and optical materials such as light guide plates and films for liquid crystal displays is progressing, and there are increasing expectations for applications that were said to be difficult to carry out molding and processing with conventional methacrylic resins.
For example, when injection molding a large-size, thin molded article, if the fluidity of the resin is poor, molding will be impossible due to insufficient injection pressure, and distortion of the molded article will increase. Consequently, a high fluidity that allows molding is desirable even if the injection pressure is low. On the other hand, there is a need for further improvement in solvent resistance and mechanical strength while maintaining the colorless transparency that methacrylic resins have and the processability of the obtained resins.
Conventionally, generally known methods for improving the mechanical strength and molding properties of a methacrylic resin have included conferring fluidity with a low molecular weight methacrylic resin, and conferring mechanical strength with a methacrylic resin having a high molecular weight or a densely crosslinked structure.
Reports related to this have included a technology that melt-mixes a high molecular weight and a low molecular weight methacrylic resin (e.g., Patent document 1), a technology that co-polymerizes a methacrylic resin formed by a low molecular weight methacrylic resin with a large amount of another vinyl monomer (e.g., Patent document 2), a technology that enlarges the molecular weight distribution by producing a densely cross-linked methacrylic resin using a polyfunctional monomer (e.g., Patent document 3), and a technology that, while maintaining mechanical strength, improves fluidity as compared to a conventional methacrylic resin by using a multistage polymerization method (e.g., Patent document 4).